<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>类选择器</title>
    <style>
        .div1 {
            color: red;
            background-color: blue;
        }
        .div2 {
            background-color: orange;
        }
    </style>
</head>
<body>
    <div class="div1">111111111111111111</div>
    <div class="div2 div1">222222222222222222</div>
</body>
</html>